Scanning probe microscopes (SPMs) are instruments that provide high resolution information about surface contours. Vertical movement of a sensing probe, in response to a raster scanning procedure of the sensing probe across a target surface, is used for determining the target surface contour. Implementations of SPM devices are based on the interaction of forces including atomic, electrical potential, magnetic, capacitive, or chemical potential to maintain a constant probe to target surface gap, or distance. One common use of these devices is imaging with some types of SPMs have the capability of imaging individual atoms.
In addition to imaging surface contours, SPMs can be used to measure a variety of physical or chemical properties with detail over the range from a few Angstroms to hundreds of microns. For these applications, SPMs can provide lateral and vertical resolution that is not obtainable from any other type of device. Examples of applications include imaging or measuring the contour properties of transistors, silicon chips, disk surface, crystals, cells, or the like.
In order to provide for optimal operation of the SPM, a scanning probe is positioned over a target surface at a distance within the same order of magnitude as molecular geometries. That is, a distance of one or two atoms, or an order of magnitude of tens of Angstroms. Prior art methods using sensing probes have typically positioned the probe manually at a desired distance from the target surface or by allowing the probe to make contact with the target surface and subsequently backing the probe away from the target surface. Such an embodiment is disclosed, for example, in U.S. Pat. No. 5,025,658.
The prior art methods of positioning the scanning probe tip have several shortcomings. The initial positioning process for tolerances in the microscopic range is one that is inherently critical. As noted, optimal scanning probe microscope operation necessitates positioning the sensing probe above the target surface at a distance within an order of magnitude of molecular geometries. The necessity of human interaction results in questionable reliability and, further, is time consuming. In addition, allowing the scanning probe to make physical contact with the target surface during calibration or set up may damage, or otherwise make unusable, the target device/substance or scanning tip.